Childrens Illustrated Encyclopedia

326

Alveolus

each alveolus is surrounded

by a network of very fine

blood vessels called capillaries.

oxygen passes from the air

space inside the alveolus,

through the lining, and into

the blood. Carbon dioxide

passes in the opposite way.

We NeeD oXYGeN To lIve, and we get oxygen by breathing

air. When we breathe in, air is sucked through the nose or mouth,

down the windpipe, and into the lungs, two powerful organs

in the chest. The lungs absorb as much oxygen from the air

as possible. The oxygen travels in the blood from the lungs

to every part of the body. our bodies use oxygen to release

energy from sugars obtained from the food we eat. This also

releases harmful carbon dioxide, which is breathed out of the

body by the lungs. The whole process is called respiration. The

lungs, together with the airways, throat,

and nasal passages, form the respiratory

system. each lung is surrounded by two thin

coverings or membranes called the pleurae.

The lungs themselves contain air tubes,

blood vessels, and millions of tiny air sacs

called alveoli. If you spread these air

sacs out flat, they would cover the area

of a tennis court.

luNGfIsh

Most animals that live on

land have lungs. Many water

animals, however, including

most fish, breathe using

feathery flaps called

gills. oxygen in the

water passes through

the thin gill coverings

to the blood inside

the fish’s body. The

lungfish shown here

is an unusual animal

because it has lungs and

gills, so it can breathe in

both ways and can survive

out of water for a long time.

BreAThING ouT

When you breathe out, the

diaphragm and chest muscles

relax. The lungs are spongy and

elastic, so they spring back to

their smaller size after they have

been stretched. This blows air

back out of the lungs.

BreAThING IN

When you breathe in, the diaphragm

contracts (becomes flatter) and pulls

down the base of the lungs. Muscles

between the ribs contract to swing

the ribs up and out. These actions

stretch and enlarge the lungs, so

that air is sucked in.

hoW We MAke souNDs

We use the air flowing in and

out of our lungs to make sounds.

We speak, shout, laugh, and cry

by making air flow over two

small leathery flaps called the

vocal cords. These are located

in the larynx (voice box), in the

lower part of the throat. Muscles

in the throat stretch the flaps

tighter to change from low

notes to high notes.

Lungs and breathing

Breathing

Find out more

Brain and nerves

heart and blood

human body

Muscles and movement

oxygen

skeletons

Trachea

(windpipe)

divides into

two main

bronchi.

Air flows in through the

nose and mouth, down

the throat, along the

trachea (windpipe),

and into the lungs.

Larynx (voice

box) at top

of trachea

Pharynx (throat)

Lung

Air with

carbon

dioxide

Air space

Oxygen-rich air inside alveolus

The alveoli are

grouped together

like bunches of

grapes. Tiny tubes

called bronchioles

bring fresh oxygen-

containing air

to the alveoli.

Diaphragm is a dome-shaped

sheet of muscle.

Bronchi continue to

branch and divide.

Bronchiole

Capillary

blood vessels

Alveolus

Lungs empty

of air as you

breathe out.

Lungs fill with air

as you breathe in.

The rib cage is flexible, so

the lungs can expand and

shrink when we breathe.

Diaphragm

relaxes and rises.

Diaphragm

contracts

and flattens.

US_326_Lungs_breathing.indd 326 09/02/16 3:57 pm